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Force inside atoms
• Electrons are bound to the nucleus by the attractive force between electrons (-) and protons (+).
ATOMIC NUMBER – equals the number of protons in an atom of an element
82
PbLead
207.2
Atomic Number
Element Card
ATOMIC NUMBER – equals the number of protons in an atom of an element
Element Atomic Number
Number of Protons
Carbon 6
Calcium 20
Silver 47
BALANCING CHARGE* the +1 charge of a proton exactly equals the -1 charge of an electron
* all atoms are electrically neutral * in an atom the number of
protons equals the number of electrons
• The number of neutrons = mass number –
atomic number
Mass Number
Number of Protons(Atomic Number)
Number of Neutrons
19 206 6
27 1366 30
• ISOTOPES – atoms of the same element have different numbers of neutrons
Isotope Mass Number
Atomic Number
Number of Protons
Number of Neutrons
Oxygen - 16 8
Oxygen - 17
Oxygen - 18